The pressure which is measured with reference to absolute vacuum pressure is
- A.gauge pressure
- B.absolute pressure
- C.atmospheric pressure
- D.absolute zero pressure
Correct answer
Explanation
The correct answer is B, absolute pressure. Pressure counted from a perfect vacuum as the zero point is called absolute pressure. A perfect vacuum holds no gas and exerts no pressure, so it is the true zero of any pressure scale. The working relation is absolute pressure = gauge pressure + atmospheric pressure, and atmospheric pressure at sea level is about 101.3 kilopascals, or 760 mm of mercury. So a tyre whose gauge reads 200 kPa is really at about 301 kPa absolute. Gas laws and thermodynamic formulas always take absolute pressure, which is why the distinction is tested. Option A is wrong because gauge pressure takes atmospheric pressure as its zero, so an open gauge reads zero even though air is pressing on it. Option C is wrong because atmospheric pressure is the weight of the air column itself, read on a barometer. Option D is wrong because 'absolute zero pressure' names the vacuum, the reference point, not the reading taken from it. Exam tip: absolute = gauge + atmospheric; a reading below atmospheric is vacuum or negative gauge pressure.
Practice Questions
View allThe fact that the planets move around the Sun, not in circles but in ellipses, was first demonstrated by
- A.Galileo
- B.Martin Luther
- C.Johannes Kepler
- D.Copernicus
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In 1609 Kepler showed that the planets move around the Sun in elliptical orbits, with the Sun at one focus of the ellipse.
Read the full explanation →Which one of the following statements is correct?
- A.Urea is produced in liver.
- B.Urea is produced in blood.
- C.Urea is produced from digestion of starch.
- D.Urea is produced in lung and kidney.
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Read the full explanation →Which one of the following is the correct sequence of passage of light in a compound microscope?
- A.Condenser-Objective lens-Eyepiece-Body tube
- B.Objective lens-Condenser-Body tube-Eyepiece
- C.Condenser-Objective lens-Body tube-Eyepiece
- D.Eyepiece-Objective lens-Body tube-Mirror
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Light passes through the condenser to the specimen, is picked up by the objective lens, travels up the body tube and reaches the eye through the eyepiece.
Read the full explanation →Which one of the following statements regarding haemoglobin is correct?
- A.Haemoglobin present in RBC can carry only oxygen but not carbon dioxide.
- B.Haemoglobin of RBC can carry both oxygen and carbon dioxide.
- C.Haemoglobin of RBC can carry only carbon dioxide.
- D.Haemoglobin is only used for blood clotting and not for carrying gases.
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Read the full explanation →Which one of the following statements regarding histone proteins is correct?
- A.Histones are proteins that are present in mitochondrial membrane.
- B.Histones are proteins that are present in nucleus in association with DNA.
- C.Histones are proteins associated with lipids in the cytosol.
- D.Histones are proteins associated with carbohydrates in the cytosol.
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They are the proteins around which DNA winds to form chromatin in the nucleus of eukaryotic cells. Histones are small basic proteins, rich in the positively charged amino acids lysine and arginine, which attract the negatively charged phosphate groups of DNA.
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